ANIMA WG S. Jiang, Ed.
Internet-Draft Z. Du
Intended status: Informational Huawei Technologies Co., Ltd
Expires: June 18, 2018 B. Carpenter
Univ. of Auckland
Q. Sun
China Telecom
December 15, 2017
Autonomic IPv6 Edge Prefix Management in Large-scale Networksdraft-ietf-anima-prefix-management-07
Abstract
This document defines two autonomic technical objectives for IPv6
prefix management at the edge of large-scale ISP networks, with an
extension to support IPv4 prefixes. An important purpose of the
document is to use it for validation of the design of various
components of the autonomic networking infrastructure.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 18, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
Jiang, et al. Expires June 18, 2018 [Page 1]

Internet-Draft Auto IPv6 Prefix Management December 2017
This document defines two autonomic technical objectives for IPv6
prefix management in large-scale networks, with an extension to
support IPv4 prefixes. The background to Autonomic Networking (AN)
is described in [RFC7575] and [RFC7576]. The GeneRic Autonomic
Signaling Protocol (GRASP) is specified by [I-D.ietf-anima-grasp] and
can make use of the proposed technical objectives to provide a
solution for autonomic prefix management. An important purpose of
the present document is to use it for validation of the design of
GRASP and other components of the autonomic networking infrastructure
described in [I-D.ietf-anima-reference-model].
This document is not a complete functional specification of an
autonomic prefix management system and it does not describe all
detailed aspects of the GRASP objective parameters and Autonomic
Service Agent (ASA) procedures necessary to build a complete system.
Instead, it describes the architectural framework utilizing the
components of the ANI, outlines the different deployment options and
aspects, and defines GRASP objectives for use in building the system.
It also provides some basic parameter examples.
This document is not intended to solve all cases of IPv6 prefix
management. In fact, it assumes that the network's main
infrastructure elements already have addresses and prefixes. The
document is dedicated to how to make IPv6 prefix management at the
edges of large-scale networks as autonomic as possible. It is
specifically written for service provider (ISP) networks. Although
there are similarities between ISPs and large enterprise networks,
the requirements for the two use cases differ. In any case, the
scope of the solution is expected to be limited, like any autonomic
network, to a single management domain.
However, the solution is designed in a general way. Its use for a
broader scope than edge prefixes, including some or all
infrastructure prefixes, is left for future discussion.
A complete solution has many aspects that are not discussed here.
Once prefixes have been assigned to routers, they need to be
communicated to the routing system as they are brought into use.
Similarly, when prefixes are released, they need to be removed from
the routing system. Different operators may have different policies
about prefix lifetimes, and they may prefer to have centralized or
distributed pools of spare prefixes. In an autonomic network, these
are properties decided by the design of the relevant ASAs. The GRASP
objectives are simply building blocks.
A particular risk of distributed prefix allocation in large networks
is that over time, it might lead to fragmentation of the address
space and an undesirable increase in the interior routing protocol
Jiang, et al. Expires June 18, 2018 [Page 3]

Internet-Draft Auto IPv6 Prefix Management December 2017
tables. The extent of this risk depends on the algorithms and
policies used by the ASAs. Mitigating this risk might even become an
autonomic function in itself.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document uses terminology defined in [RFC7575].
3. Problem Statement
The autonomic networking use case considered here is autonomic IPv6
prefix management at the edge of large-scale ISP networks.
Although DHCPv6 Prefix Delegation [RFC3633] supports automated
delegation of IPv6 prefixes from one router to another, prefix
management still largely depends on human planning. In other words,
there is no basic information or policy to support autonomic
decisions on the prefix length that each router should request or be
delegated, according to its role in the network. Roles could be
defined separately for individual devices or could be generic (edge
router, interior router, etc.). Furthermore, IPv6 prefix management
by humans tends to be rigid and static after initial planning.
The problem to be solved by autonomic networking is how to
dynamically manage IPv6 address space in large-scale networks, so
that IPv6 addresses can be used efficiently. Here, we limit the
problem to assignment of prefixes at the edge of the network, close
to access routers that support individual fixed-line subscribers,
mobile customers, and corporate customers. We assume that the core
infrastructure of the network has already been established with
appropriately assigned prefixes. The AN approach discussed in this
document is based on the assumption that there is a generic discovery
and negotiation protocol that enables direct negotiation between
intelligent IP routers. GRASP [I-D.ietf-anima-grasp] is intended to
be such a protocol.
3.1. Intended User and Administrator Experience
The intended experience is, for the administrators of a large-scale
network, that the management of IPv6 address space at the edge of the
network can be run with minimum effort, as devices at the edge are
added and removed and as customers of all kinds join and leave the
Jiang, et al. Expires June 18, 2018 [Page 4]

Internet-Draft Auto IPv6 Prefix Management December 2017
network. In the ideal scenario, the administrators only have to
specify a single IPv6 prefix for the whole network and the initial
prefix length for each device role. As far as users are concerned,
IPv6 prefix assignment would occur exactly as it does in any other
network.
The actual prefix usage needs to be logged for potential offline
management operations including audit and security incident tracing.
3.2. Analysis of Parameters and Information Involved
For specific purposes of address management, a few parameters are
involved on each edge device (some of them can be pre-configured
before they are connected). They include:
o Identity, authentication and authorization of this device. This
is expected to use the autonomic networking secure bootstrap
process [I-D.ietf-anima-bootstrapping-keyinfra], following which
the device could safely take part in autonomic operations.
o Role of this device. Some example roles are discussed in
Section 6.1.
o An IPv6 prefix length for this device.
o An IPv6 prefix that is assigned to this device and its downstream
devices.
A few parameters are involved in the network as a whole. They are:
o Identity of a trust anchor, which is a certification authority
(CA) maintained by the network administrators, used during the
secure bootstrap process.
o Total IPv6 address space available for edge devices. It is a pool
of one or several IPv6 prefixes.
o The initial prefix length for each device role.
3.2.1. Parameters each device can define for itself
This section identifies those of the above parameters that do not
need external information in order for the devices concerned to set
them to a reasonable default value after bootstrap or after a network
disruption. There are few of these:
o Default role of this device.
Jiang, et al. Expires June 18, 2018 [Page 5]

Internet-Draft Auto IPv6 Prefix Management December 2017
o Default IPv6 prefix length for this device.
o Cryptographic identity of this device, as needed for secure
bootstrapping [I-D.ietf-anima-bootstrapping-keyinfra].
The device may be shipped from the manufacturer with pre-configured
role and default prefix length, which could be modified by an
autonomic mechanism. Its cryptographic identity will be installed by
its manufacturer.
3.2.2. Information needed from network operations
This section identifies those parameters that might need operational
input in order for the devices concerned to set them to a non-default
value.
o Non-default value for the IPv6 prefix length for this device.
This needs to be decided based on the role of this device.
o The initial prefix length for each device role.
o Whether to allow the device to request more address space.
o The policy when to request more address space, for example, if the
address usage reaches a certain limit or percentage.
3.2.3. Comparison with current solutions
This section briefly compares the above use case with current
solutions. Currently, the address management is still largely
dependent on human planning. It is rigid and static after initial
planning. Address requests will fail if the configured address space
is used up.
Some autonomic and dynamic address management functions may be
achievable by extending the existing protocols, for example,
extending DHCPv6-PD (DHCPv6 Prefix Delegation, [RFC3633]) to request
IPv6 prefixes according to the device role. However, defining
uniform device roles may not be a practical task. Some functions are
not suitable to be achieved by any existing protocols.
Using a generic autonomic discovery and negotiation protocol instead
of specific solutions has the advantage that additional parameters
can be included in the autonomic solution without creating new
mechanisms. This is the principal argument for a generic approach.
Jiang, et al. Expires June 18, 2018 [Page 6]

Internet-Draft Auto IPv6 Prefix Management December 20173.3. Interaction with other devices3.3.1. Information needed from other devices
This section identifies those of the above parameters that need
external information from neighbor devices (including the upstream
devices). In many cases, two-way dialogue with neighbor devices is
needed to set or optimize them.
o Identity of a trust anchor.
o The device will need to discover a device, from which it can
acquire IPv6 address space.
o The initial prefix length for each device role, particularly for
its own downstream devices.
o The default value of the IPv6 prefix length may be overridden by a
non-default value.
o The device will need to request and acquire one or more IPv6
prefixes that can be assigned to this device and its downstream
devices.
o The device may respond to prefix delegation requests from its
downstream devices.
o The device may require to be assigned more IPv6 address space, if
it used up its assigned IPv6 address space.
3.3.2. Monitoring, diagnostics and reporting
This section discusses what role devices should play in monitoring,
fault diagnosis, and reporting.
o The actual address assignments need to be logged for potential
offline management operations.
o In general, the usage situation of address space should be
reported to the network administrators, in an abstract way, for
example, statistics or visualized report.
o A forecast of address exhaustion should be reported.
Jiang, et al. Expires June 18, 2018 [Page 7]

Internet-Draft Auto IPv6 Prefix Management December 20174. Autonomic Edge Prefix Management Solution
This section introduces the building blocks for an autonomic edge
prefix management solution. As noted in Section 1, this is not a
complete description of a solution, which will depend on the detailed
design of the relevant Autonomic Service Agents. It uses the generic
discovery and negotiation protocol defined by [I-D.ietf-anima-grasp].
The relevant GRASP objectives are defined in Section 5.
The procedures described below are carried out by an Autonomic
Service Agent (ASA) in each device that participates in the solution.
We will refer to this as the PrefixManager ASA.
4.1. Behaviors on prefix requesting device
If the device containing a PrefixManager ASA has used up its address
pool, it can request more space according to its requirements. It
should decide the length of the requested prefix and request it by
the mechanism described in Section 6. Note that although the
device's role may define certain default allocation lengths, those
defaults might be changed dynamically, and the device might request
more, or less, address space due to some local operational heuristic.
A PrefixManager ASA that needs additional address space should
firstly discover peers that may be able to provide extra address
space. The ASA should send out a GRASP Discovery message that
contains a PrefixManager Objective option (see Section 5.1) in order
to discover peers also supporting that option. Then it should choose
one such peer, most likely the first to respond.
If the GRASP discovery Response message carries a divert option
pointing to an off-link PrefixManager ASA, the requesting ASA may
initiate negotiation with that ASA diverted device to find out
whether it can provide the requested length prefix.
In any case, the requesting ASA will act as a GRASP negotiation
initiator by sending a GRASP Request message with a PrefixManager
Objective option. The ASA indicates in this option the length of the
requested prefix. This starts a GRASP negotiation process.
During the subsequent negotiation, the ASA will decide at each step
whether to accept the offered prefix. That decision, and the
decision to end negotiation, is an implementation choice.
The ASA could alternatively initiate rapid mode GRASP discovery with
an embedded negotiation request, if it is implemented.
Jiang, et al. Expires June 18, 2018 [Page 8]

Internet-Draft Auto IPv6 Prefix Management December 20174.2. Behaviors on prefix providing device
At least one device on the network must be configured with the
initial pool of available prefixes mentioned in Section 3.2. Apart
from that requirement, any device may act as a prefix providing
device.
A device that receives a Discovery message with a PrefixManager
Objective option should respond with a GRASP Response message if it
contains a PrefixManager ASA. Further details of the discovery
process are described in [I-D.ietf-anima-grasp]. When this ASA
receives a subsequent Request message, it should conduct a GRASP
negotiation sequence, using Negotiate, Confirm-waiting, and
Negotiation-ending messages as appropriate. The Negotiate messages
carry a PrefixManager Objective option, which will indicate the
prefix and its length offered to the requesting ASA. As described in
[I-D.ietf-anima-grasp], negotiation will continue until either end
stops it with a Negotiation-ending message. If the negotiation
succeeds, the prefix providing ASA will remove the negotiated prefix
from its pool, and the requesting ASA will add it. If the
negotiation fails, the party sending the Negotiation-ending message
may include an error code string.
During the negotiation, the ASA will decide at each step how large a
prefix to offer. That decision, and the decision to end negotiation,
is an implementation choice.
The ASA could alternatively negotiate in response to rapid mode GRASP
discovery, if it is implemented.
This specification is independent of whether the PrefixManager ASAs
are all embedded in routers, but that would be a rather natural
scenario. In a hierarchical network topology, a given router
typically provide prefixes for routers below it in the hierarchy, and
it is also likely to contain the first PrefixManager ASA discovered
by those downstream routers. However, the GRASP discovery model,
including its Redirect feature, means that this is not an exclusive
scenario, and a downstream PrefixManager ASA could negotiate a new
prefix with a device other than its upstream router.
A resource shortage may cause the gateway router to request more
resource in turn from its own upstream device. This would be another
independent GRASP discovery and negotiation process. During the
processing time, the gateway router should send a Confirm-waiting
Message to the initial requesting router, to extend its timeout.
When the new resource becomes available, the gateway router responds
with a GRASP Negotiate message with a prefix length matching the
request.
Jiang, et al. Expires June 18, 2018 [Page 9]

Internet-Draft Auto IPv6 Prefix Management December 2017
The algorithm to choose which prefixes to assign on the prefix
providing devices is an implementation choice.
4.3. Behavior after Successful Negotiation
Upon receiving a GRASP Negotiation-ending message that indicates that
an acceptable prefix length is available, the requesting device may
use the negotiated prefix without further messages.
There are use cases where the ANI/GRASP based prefix management
approach can work together with DHCPv6-PD [RFC3633] as a complement.
For example, the ANI/GRASP based method can be used intra-domain,
while the DHCPv6-PD method works inter-domain (i.e., across an
administrative boundary). Also, ANI/GRASP can be used inside the
domain, and DHCP/DHCPv6-PD be used on the edge of the domain to
client (non-ANI devices). Another similar use case would be ANI/
GRASP inside the domain, with RADIUS [RFC2865] providing prefixes to
client devices.
4.4. Prefix logging
Within the autonomic prefix management, all the prefix assignment is
done by devices without human intervention. It may be required to
record all the prefix assignment history, for example to detect or
trace lost prefixes after outages, or to meet legal requirements.
However, the logging and reporting process is out of scope for this
document.
5. Autonomic Prefix Management Objectives
This section defines the GRASP technical objective options that are
used to support autonomic prefix management.
5.1. Edge Prefix Objective Option
The PrefixManager Objective option is a GRASP objective option
conforming to [I-D.ietf-anima-grasp]. Its name is "PrefixManager"
(see Section 8) and it carries the following data items as its value:
the prefix length, and the actual prefix bits. Since GRASP is based
on CBOR (Concise Binary Object Representation [RFC7049]), the format
of the PrefixManager Objective option is described as follows in CBOR
data definition language (CDDL) [I-D.ietf-cbor-cddl]:
Jiang, et al. Expires June 18, 2018 [Page 10]

Internet-Draft Auto IPv6 Prefix Management December 2017
objective = ["PrefixManager", objective-flags, loop-count,
[length, ?prefix]]
loop-count = 0..255 ; as in the GRASP specification
objective-flags /= ; as in the GRASP specification
length = 0..128 ; requested or offered prefix length
prefix = bytes .size 16 ; offered prefix in binary format
The use of the 'dry run' mode of GRASP is NOT RECOMMENDED for this
objective, because it would require both ASAs to store state about
the corresponding negotiation, to no real benefit - the requesting
ASA cannot base any decisions on the result of a successful dry run
negotiation.
5.2. IPv4 extension
This section presents an extended version of the PrefixManager
Objective that supports IPv4 by adding an extra flag:
objective = ["PrefixManager", objective-flags, loop-count, prefval]
loop-count = 0..255 ; as in the GRASP specification
objective-flags /= ; as in the GRASP specification
prefval /= pref6val
pref6val = [version6, length, ?prefix]
version6 = 6
length = 0..128 ; requested or offered prefix length
prefix = bytes .size 16 ; offered prefix in binary format
prefval /= pref4val
pref4val = [version4, length4, ?prefix4]
version4 = 4
length4 = 0..32 ; requested or offered prefix length
prefix4 = bytes .size 4 ; offered prefix in binary format
Prefix and address management for IPv4 is considerably more difficult
than for IPv6, due to the prevalence of NAT, ambiguous addresses
[RFC1918], and address sharing [RFC6346]. These complexities might
require further extending the objective with additional fields which
are not defined by this document.
6. Prefix Management Parameters
An implementation of a prefix manager MUST include default settings
of all necessary parameters. However, within a single administrative
domain, the network operator MAY change default parameters for all
devices with a certain role. Thus it would be possible to apply an
Jiang, et al. Expires June 18, 2018 [Page 11]

Internet-Draft Auto IPv6 Prefix Management December 2017
intended policy for every device in a simple way, without traditional
configuration files. As noted in Section 4.1, individual autonomic
devices may also change their own behavior dynamically.
For example, the network operator could change the default prefix
length for each type of role. A prefix management parameters
objective, which contains mapping information of device roles and
their default prefix lengths, MAY be flooded in the network, through
the Autonomic Control Plane (ACP)
[I-D.ietf-anima-autonomic-control-plane]. The objective is defined
in CDDL as follows:
objective = ["PrefixManager.Params", objective-flags, any]
loop-count = 0..255 ; as in the GRASP specification
objective-flags /= ; as in the GRASP specification
The 'any' object would be the relevant parameter definitions (such as
the example below) transmitted as a CBOR object in an appropriate
format.
This could be flooded to all nodes, and any PrefixManager ASA that
did not receive it for some reason could obtain a copy using GRASP
unicast synchronization. Upon receiving the prefix management
parameters, every device can decide its default prefix length by
matching its own role.
6.1. Example of Prefix Management Parameters
The parameters comprise mapping information of device roles and their
default prefix lengths in an autonomic domain. For example, suppose
an IPRAN (IP Radio Access Network) operator wants to configure the
prefix length of Radio Network Controller Site Gateway (RSG) as 34,
the prefix length of Aggregation Site Gateway (ASG) as 44, and the
prefix length of Cell Site Gateway (CSG) as 56. This could be
described in the value of the PrefixManager.Params objective as:
[
[["role", "RSG"],["prefix_length", 34]],
[["role", "ASG"],["prefix_length", 44]],
[["role", "CSG"],["prefix_length", 56]]
]
This example is expressed in JSON notation [RFC7159], which is easy
to represent in CBOR.
Jiang, et al. Expires June 18, 2018 [Page 12]

Internet-Draft Auto IPv6 Prefix Management December 2017
An alternative would be to express the parameters in YANG [RFC7950]
using the YANG-to-CBOR mapping [I-D.ietf-core-yang-cbor].
For clarity, the background of the example is introduced below, which
can also be regarded as a use case of the mechanism proposed in this
document.
An IPRAN network is used for mobile backhaul, including radio
stations, RNC (in 3G) or the packet core (in LTE), and the IP network
between them as shown in Figure 1. The eNB (Evolved Node B), RNC
(Radio Network Controller), SGW (Service Gateway), and MME (Mobility
Management Entity) are mobile network entities defined in 3GPP. The
CSG, ASG, and RSG are entities defined in the IPRAN solution.
The IPRAN topology shown in Figure 1 includes Ring1 which is the
circle following ASG1->RSG1->RSG2->ASG2->ASG1, Ring2 following
CSG1->ASG1->ASG2->CSG2->CSG1, and Ring3 following
CSG3->ASG1->ASG2->CSG3. In a real deployment of IPRAN, there may be
more stations, rings, and routers in the topology, and normally the
network is highly dependent on human design and configuration, which
is neither flexible nor cost-effective.
+------+ +------+
| eNB1 |---| CSG1 |\
+------+ +------+ \ +-------+ +------+ +-------+
| \ | ASG1 |-------| RSG1 |-----------|SGW/MME|
| Ring2 +-------+ +------+ \ /+-------+
+------+ +------+ / | | \ /
| eNB2 |---| CSG2 | \ / | Ring1 | \/
+------+ +------+ \ Ring3| | /\
/ \ | | / \
+------+ +------+ / \ +-------+ +------+/ \+-------+
| eNB3 |---| CSG3 |--------| ASG2 |------| RSG2 |---------| RNC |
+------+ +------+ +-------+ +------+ +-------+
Figure 1: IPRAN Topology Example
If ANI/GRASP is supported in the IPRAN network, the network nodes
should be able to negotiate with each other, and make some autonomic
decisions according to their own status and the information collected
from the network. The Prefix Management Parameters should be part of
the information they communicate.
The routers should know the role of their neighbors, the default
prefix length for each type of role, etc. An ASG should be able to
request prefixes from an RSG, and an CSG should be able to request
prefixes from an ASG. In each request, the ASG/CSG should indicate
Jiang, et al. Expires June 18, 2018 [Page 13]

Internet-Draft Auto IPv6 Prefix Management December 2017
the devices and enables the use of GRASP[I-D.ietf-anima-grasp] not
only for p2p communication, but also for distribution/flooding.
The central devices and edge routers run software in the form of
"Autonomic Service Agents" (ASA) to support this document's autonomic
IPv6 edge prefix management (PM). The ASAs for prefix management are
called PM-ASAs below, and together comprise the Autonomic Prefix
Management Function.
Edge routers can have different roles based on the type and number of
CPE attaching to them. Each edge router could be an RSG, ASG, or CSG
in mobile aggregation networks (see Section 6.1). Mechanisms outside
the scope of this document make routers aware of their roles.
Some considerations about the proposed deployment model are listed as
follows.
1. In a minimum Prefix Management solution, the central device uses
the "PrefixManager.Params" GRASP Objective introduced in this
document to disseminate network wide, per-role parameters to edge
routers. The PM-ASA uses the parameters applying to its role to
locally configure pre-existing addressing functions. Because PM-ASA
does not manage the dynamic assignment of actual IPv6 address
prefixes in this case, the following options can be considered:
1.a The edge router connects via downstream interfaces to (host) CPE
that each requires an address. The PM-ASA sets up for each such
interface a DHCP requesting router (according to [RFC3633]) to
request an IPv6 prefix for the interface. The router's address on
the downstream interface can be another parameter from the GRASP
Objective. The CPEs assign addresses in the prefix via RAs from the
router or the PM-ASA manages a local DHCPv6 server to assign
addresses to the CPEs. A central DHCP server acting as the DHCP
delegating router (according to [RFC3633]) is required. Its address
can be another parameter from the GRASP Objective.
1.b The edge router also connects via downstream interfaces to
(customer managed) CPEs that are routers and act as DHCPv6 requesting
routers. The need to support this could be derived from role and/or
GRASP parameters and the PM-ASA sets up a DHCP relay function to pass
on requests to the central DHCP server as in 1.a.
2. In a solution without a central DHCP server, the PM-ASA on the
edge routers not only learn parameters from "PrefixManager.Params"
but also utilize GRASP to request/negotiate actual IPv6 prefix
delegation via the GRASP "PrefixManager" objective described in more
detail below. In the most simple case, these prefixes are delegated
via this GRASP objective from the PM-ASA in the central device. This
Jiang, et al. Expires June 18, 2018 [Page 20]

Internet-Draft Auto IPv6 Prefix Management December 2017
device must be provisioned initially with a large pool of prefixes.
The delegated prefixes are then used by the PM-ASA on the edge
routers to edge routers to configure prefixes on their downstream
interfaces to assign addresses via RA/SLAAC to host CPEs. The PM-ASA
may also start local DHCP servers (as in 1.a) to assign addresses via
DHCP to CPE from the prefixes it received. This includes both host
CPEs requesting IPv6 addresses as well as router CPEs that request
IPv6 prefixes. The PM-ASA needs to manage the address pool(s) it has
requested via GRASP and allocate sub-address pools to interfaces and
the local DHCP servers it starts. It needs to monitor the address
utilization and accordingly request more address prefixes if its
existing prefixes are exhausted, or return address prefixes when they
are unneeded.
This solution is quite similar to the initial described IPv6 DHCP
deployment model without central DHCP server, and ANI/ACP/GRASP and
the PM-ASA do provide the automation to make this approach work more
easily than it is possible today.
3. The address pool(s) from which prefixes are allocated does not
need to be taken all from one central location. Edge router PM-ASA
that received a big (short) prefix from a central PM-ASA could offer
smaller sub-prefixes to neighboring edge-router PM-ASA. GRASP could
be used in such a way that the PM-ASA would find and select the
objective from the closest neighboring PM-ASA, therefore allowing to
maximize aggregation: A PM-ASA would only request further (smaller/
shorter) prefixes when it exhausts its own poll (from the central
location) and can not get further large prefixes from that central
location anymore. Because the overflow prefixes taken from a
topological nearby PM-ASA, the number of longer prefixes that have to
be injected into the routing tables is limited and the topological
proximity increases the chances that aggregation of prefixes in the
IGP can most likely limit the geography in which the longer prefixes
need to be routed.
4. Instead of peer-to-peer optimization of prefix delegation, a
hierarchy of PM-ASA can be built (indicated in the picture via a
dotted intermediate router). This would require additional
parameters to the "PrefixManager" objective to allow creating a
hierarchy of PM-ASA across which the prefixes can be delegated. This
is not detailed further below.
5. In cases where CPEs are also part of the ANI Domain (e.g.,
"Managed CPE"), then GRASP will extend into the actual customer sites
and can equally run a PM-ASA. All the options described in points 1
to 4 above would then apply to the CPE as the edge router with the
mayor changes being that a) a CPE router will most likley not need to
run DHCPv6-PD itself, but only DHCP address assignment, b) The edge
Jiang, et al. Expires June 18, 2018 [Page 21]